Legislation introduced by the previous Government to clamp down on legal highs was "rushed" and without thorough consultation, argues a researcher who has examined the process.
Massey University's Dr Marta Rychert said the Psychoactive Substances Act (PSA), implemented in 2013, was also an important piece of law that could have implications for how the legalisation of cannabis could be rolled out, should the Government go down that path.
The PSA established the world's first regulated legal market for "new drugs" and received significant international attention as an innovative, bold and balanced response.
But Rychert said the implementation process had turned out to be problematic.
"My research shows that a rushed policy process, without thorough consultation with communities or key stakeholders, may have dramatic implications for the success of the law change."
Rather than criminalising the market and banning products, the PSA aimed to regulate synthetic drug manufacturers who had to prove their products were safe.
Of the 350 different synthetic drugs on sale in New Zealand at the time, around 41 were allowed to stay on shop shelves as they were deemed safe enough for an interim exemption.
Those products were later banned after public outcry.
"The ban inadvertently pushed synthetic drugs underground and handed power over to a black market," she said.
"Sadly, in recent months, more than 20 people have died, most probably due to the use of illegal synthetic cannabis.
"The original legislation aimed to prevent this type of situation by putting in place manufacturing and quality standards and retail regulations."
Her just-published PhD study explored why the innovative response to synthetic highs didn't proceed as planned, and found a number of problems, both in terms of how the law was designed and implemented.
She said the law failed to include any price control provisions, such as excise tax, and this facilitated "price wars" among operators.
"As the market commercialised, the industry used strategies previously observed in research on alcohol and tobacco sectors – for example the promotion of products targeting vulnerable, younger customers," she said.
"This has important implications for public health.
"The time, resources and planning required to successfully implement the Psychoactive Substances Act also appeared to be underestimated."
Public submissions are currently under way for the Psychoactive Substances (Increasing Penalty for Supply and Distribution) Amendment Bill.
The bill proposes to increase the maximum penalty for people who illegally supply psychoactive substances from two years to eight years.
It recently passed its first reading in Parliament in a 65 to 55 vote.
Labour and the Greens opposed increasing jail time for suppliers of synthetic drugs, but National and New Zealand First voted in favour of the change.
Rychert believed her research could help shape future discussions around legalising cannabis in New Zealand.
"In the last five years or so, parts of the US, Canada and Uruguay have legalised cannabis for recreational use and it's anticipated that more countries will follow, including New Zealand which is due to have a referendum on cannabis law reform by 2020.
"If policy change follows, we need to make sure the regime we implement will best serve the benefits of legalisation and, at the same time, prevent an increase in substance dependence."